Arrangements for securing aircraft cargo doors in their openings using latch pins and latch cams have been known for many years. These arrangements typically include a latch pin mounted within a latch fitting that is secured to the threshold of the cargo door opening. The latch cam is mounted to the door. When the cargo door is closed, the latch cam captures the latch pin. When the latch cam is rotated about the latch pin axis, the latch cam is pulled into tight fit with the latch pin, and the cargo door is secured in the door opening.
To properly secure a door within an opening using one or more latch mechanisms, it is desirable to mount each latch fitting at the door opening such that the latch pin, which is inserted in and carried by the latch fitting, is uniformly arranged concentrically within each of the latch cams. This is to insure that each of the latch fittings, latch pins, and latch cams carries an equal load.
Concentricity of a latch pin relative to the bore within a latch cam is particularly important when using a plurality of latch fittings and latch cams. Such an arrangement typically is used to secure aircraft cargo doors within the door openings. The problem of how to determine concentricity between a latch pin and a latch cam “within an allowable tolerance” has always existed. Determinations such as these generally require access to the latch fittings once they are secured to the door opening.
On some aircraft, the design of the cargo door and the door opening provided adequate access to the fittings when the door was closed. To determine whether a latch pin and latch cam were separated by an appropriate gap, a mechanic merely slid a feeler gauge around the latch pin. If the gauge didn't clear, the mechanic would be able to visually determine why not. On other aircraft, such as a Boeing 777, the access is limited and other measuring methods were required. Structures prevent a mechanic from having sufficient access to take measurements on the fittings, and while the measurements are possible, they are very time consuming to obtain and not very accurate.
A device and method are therefore needed to measure the concentricity of one member, such as a latch pin, relative to a second member, such as a latch cam, to enable adjustment of the mounting device for the one member so that any deficiency in concentricity can be easily corrected, regardless of the lack of physical space to work within.